And now, that health scare at yosemite national park 4 million people visit each other. But tonight, a rare and deadly virus traced to a campsite in the park. And here's abc's neal karlinsky. Reporter: Tonight, yosemite national park is ground zero for deadly outbreak of hantavirus. Already four confirmed cases, two of them fatal, leaving park officials with the enormous job of contacting the 1,700 people who stayed in yosemite's curry village campground since june. Both of these people, a male and a female, are not related, were not up here together staying in these cabins. Reporter: The virus is spread by rodent droppings, often as tiny airborne particles are ingested or breathed in. Early symptoms can take up to six weeks to appear and include fatigue, fever and chills. But in less than ten days those symptoms give way to coughing and breathing problems, as it's lungs fill with fluid. The centers for disease control is asking health departments nationwide to be on the lookout for suspected cases. Neal karlinsky, abc news, seattle.

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